1. Field of the Invention
This invention relates to a universal joint for a fluid conduit and particularly to a bellows sealed universal joint capable of angulating through 360.degree., such as is used in a pipe or ducting carrying a fluid, particularly air, for example ducted hot air in an aircraft, to cater for thermal expansion, installation tolerances and vibration.
2. Description of the Prior Art
When an internal pressure is applied to the bellows an end load is produced which must be restrained to prevent stretching of the bellows and damage to adjacent structures. Therefore, it is known to sealingly secure cylindrical ends of the bellows in respective tubular connectors adapted to be sealingly secured to two adjacent parts of the conduit, and to provide externally of the tubular connectors means for transmitting end load between the connectors whilst allowing the connectors to angulate through 360.degree..
In one known form of universal joint of this type, which is widely used in aircraft, the external load transmitting means comprises a ring with two pairs of diametrically opposed pins at right angles to each other, one pair of pins serving as pivotal connections with one tubular connector and the other pair of pins serving as pivotal connections with the other tubular connector, and the adjacent ends of the tubular connectors are profiled to afford sufficient clearance between them to permit angulation through 360.degree.. The disadvantage of this form of universal joint is that the profiled annular gap between the tubular connectors allows ingress of dust and debris which may restrict the freedom of the bellows, and, in the event of leaking of the bellows, allows egress of fluid rapidly from the joint.
Therefore, in another known form of universal joint of the bellows sealed type, which has recently been adopted in aircraft and is described in U.K. Patent Application No. 2,029,537A, the tubular connectors are formed with spherically shaped portions slidingly interfitted one within the other outside the bellows to form a "knuckle joint" capable of angulating through 360.degree., and the external load transmitting means comprises a sleeve extending beyond both interfitted portions and provided with bearing means between end portions of the sleeve and the respective connectors, the bearing means comprising, for each connector, diametrically oppositely disposed pivotable connections, with the pivotable connections of one of the connectors angularly displaced by 90.degree. from such connections on the other connector. The sleeve and the interfitted, spherically shaped portions of the connectors serve to prevent ingress of dust and debris to the bellows, and close interfitting of the spherically-shaped portions of the connectors greatly restricts egress of fluid from the joint in the event of leaking of the bellows. In one embodiment the pivotable connections are formed by interengaging curved flanges on brackets secured respectively on the sleeve and on the respective connectors, and two pairs of diametrically opposed inwardly directed pins at right-angles to each other are secured to the sleeve and extend, with clearance, into apertures in the interfitted portions of the connectors to assist angulation. The disadvantage of this form of universal joint is that it has a large number of parts which add considerably to its weight and cost, including complications in assembling it.